The present invention relates to a flying spot scanning system for communicating video information to a scanned medium, and more particularly to an optical system for a scanning system comprising a rotating polyhedron mirror for controlling a scanning laser beam.
Recently, improved recording devices, the so-called "laser printers" have been gaining popularity and have been meeting with commercial success. The major performance of "laser printers" is that visual data such as letters and pictures etc. derived from a computer, a word processor, and a facsimile device etc. are imparted to a scanned medium in the form of an electrostatic charge pattern. A laser beam functions as scanning light.
An example of the "laser printers" is desclosed in Starkweather, U.S. Pat. No. 4,034,408 issued July 5, 1977, entitled "Flying Spot Scanner". The disclosure of this patent is incorporated herein by reference.
However, in the conventional laser printers, a He-Ne gas laser is provided in which case any acousto-optical modulator is needed for modulating a laser beam in conformance with video signal information as disclosed in U.S. Pat. No. 4,034,408. The provision of the acousto-optical modulator resulted in loss of the laser beam when a laser device with a high intensity laser beam is needed.
To eliminate the need for such a modulator, a conventional laser printer comprising a semiconductor laser diode has been investigated. The conventional laser printer requires a colimeter lens, a beam expander lens and an f-.theta. characteristics imaging lens (f: focal lengh .theta.: inclination angle) which are very costly to thereby make the laser printer expensive and to prevent practicability of this printer.
Thus, it is desired to develop at practicable cost laser printers comprising the semiconductor laser diodes.
Further, in the above conventional laser printer, a complicated adjustment is needed to adjust the lens, especially, in the beam expander lens. That is because the beam expander lens is composed of a cylindrical lens and the longitudinal side of the cylindrical lens must be kept a constant angle against the horizontal plane. Therefore, to adjust the beam expander lens, the beam expander lens must not be rotated to move the lens.
In addition, adjustment of the distance between the respective lenses in the conventional optical system is rather complicated.
Therefore, it is further desired to develop an improved optical system for a laser printer in which adjustment of the lenses involved therein is simple.